1. Field of the Invention
The invention relates to an integrator-filter circuit for filtering a push-pull signal by means of at least two integrator signal filters comprising integrator elements, having filter frequencies adjustable by means of control currents applied to the integrator elements.
2. Description of the Related Art
In such integrator-filter circuits, which are known as such, for example, from the Philips IC TDA 9715, it is often desirable to change the filter frequencies of the integrator signal filters. For example, if the push-pull signal to be filtered is a video signal comprising a plurality of sound signals modulated on a plurality of sound carriers, these sound carriers may have different frequencies, dependent on the transmission standard. If the integrator signal filters of such an integrator-filter circuit are implemented for different sound carrier frequencies, the filter frequencies of these signal filters must be varied in dependence upon the frequencies of the sound carriers. The mutual distance between the sound carrier frequencies then mostly remains constant, but, for example, all filter frequencies must be shifted 1 MHz up or down. In state-of-the-art arrangements, this is done by adjusting the control currents applied to the integrator elements of the integrator signal filters accordingly. The control currents for the integrator elements are varied individually. This involves quite a considerable number of circuit components.